At present, with the continuous development of a microwave technology in the field of communications, the microwave technology will develop from an existing Frequency Division Duplex (FFD) system to an Intra-frequency Full Duplex (IFD) system. The frequency division duplex system refers to: a system related to the microwave technology, where the system uses different frequencies for sending and receiving signals. The intra-frequency full duplex system refers to: a system related to the microwave technology, where the system uses a same frequency for sending and receiving signals. Certainly, using the IFD system achieves a better effect than using the FDD system, and can double bandwidth. At present, the IFD system has become one of the development trends of the microwave technology.
However, in the IFD system, a signal received by the system is a mixed signal of a peer transmit signal and a local transmit signal, and due to the defect of a relative delay between the two signals caused by different transmission distances, the system cannot perform pilot-based channel estimation, and therefore cannot perform channel initialization and phase noise suppression. For example, in FIG. 1, a case in which a transceiver 1 receives signals is described. The transceiver 1 is divided into a receiver 1 and a transmitter 1. The receiver 1 may receive a signal transmitted by the transmitter 1 (that is, a local transmit signal). In addition, assuming that a receiver 2 and a transmitter 2 are provided, the receiver 1 may further receive a signal transmitted by the transmitter 2 (that is, a peer transmit signal). Transmission distances of the two signals are different, and therefore, a relative delay exists when the receiver 1 receives the two signals. Then, during channel estimation, the channel estimation cannot be performed based on pilots, and therefore, subsequent steps such as channel initialization and phase noise suppression cannot be performed.
In order to solve the foregoing defect that channel estimation cannot be performed due to a delay, the following solution is used in the prior art.
Primarily, a manner of offline delay alignment is used for processing. Referring to FIG. 1, two transceivers are described in FIG. 1, and the two transceivers have respective delays. It is assumed that periods of time of delays of the two transceivers are −T1 and −T2, respectively, where the minus indicates a delay. If the two transceivers are compensated according to T1 and T2, theoretically, no delay occurs between the two transceivers. Specifically, the delay of the transceiver 1 is −T1, and the delay of the transceiver 2 is −T2. That is, when the transceiver 1 processes a signal, an overall delay of a time −T1 occurs, and when the transceiver 2 processes a signal, an overall delay of a time −T2 occurs. Assuming that the transceiver 1 processes a signal at the moment of 0.5 seconds, and a delay of the transceiver 1 is 0.4 seconds, then a signal processing time of the transceiver 1 is actually 0.9 seconds. Assuming that the transceiver 2 processes a signal at the moment of 0.5 seconds, and a delay of the transceiver 2 is 0.2 seconds, then a signal processing time of the transceiver 2 is actually 0.7 seconds. In this case, if the transceiver 1 is compensated according to 0.4 seconds, and the transceiver 2 is compensated according to 0.2 seconds, the two transceivers both process the signal at the moment of 0.5 seconds, and no delay occurs.
However, this method has the following defects:
As shown in FIG. 2, FIG. 2 describes a process of signal transmission between the transceiver 1 and the transceiver 2. In the IFD system, it is assumed that the receiver 1 needs a time T2 to receive a signal from the transmitter 1, and needs a time T1 to receive a signal from the transmitter 2, where generally, T1>T2, a delay time of the transmitter 1 is D1, a delay time of the receiver 1 is D2, a delay of the transmitter 2 is D3, and a delay of the receiver 2 is D4.
If the receiver 1 is used as a reference, it takes a time of D1+T2+D2 for the receiver 1 to receive the signal from transmitter 1, and it takes a time of D3+T1+D2 for the receiver 1 to receive the signal from the transmitter 2. When the two have a same transmission time, D1+T2+D2=D3+T1+D2, and after calculation, it is concluded that D1=D3+T1−T2.
In this case, a delay for receiving the signal from the transmitter 1 by the receiver 2 is: D1+D4+T1, and after calculation by substituting D1 into D1+D4+T1, it is obtained that the delay is: 2T1−T2+D4+D3. The receiver 2 needs a time T2 to receive the transmitter 2, and therefore, a delay for receiving the signal from the transmitter 2 by the receiver 2 is: D3+T2+D4. If delays of two signals received by the receiver 2 are the same, 2T1−T2+D4+D3=D3+T2+D4, and a result obtained by calculation is T1=T2; this result is inconsistent with T1>T2 described above. Therefore, this solution cannot solve the problem encountered by the IFD system.
In conclusion, the IFD system in the prior art has a technical problem that the system cannot perform channel estimation due to the defect of a relative delay caused by signal transmission distances.